Limit switch



April 1949- G. c. Bless 2,466,077

LIMIT SWITCH Filed June 7, 1945 G/nn C. 5/9575 wwaw Patented Apr. 5, 1949 LIMIT SWITCH Glenn C. Biggs, Pittsburgh, Pa., assignor, by mesne assignments, to the United States of America as represented by the United States Atomic Energy Commission Application June 7, 1945, Serial No. 598,013

This invention relates to operating levers for various types of equipment and is more particularly concerned with levers that are required to operate in magnetic fields.

It is often desirable to provide operating arms for limit switches or the like that are mounted on movable equipment in such a wa that, upon predetermined movement of such equipment, the operating arm will engage a fixed surface and will be displaced thereby to bring about the rotation of a shaft or the like in order to set a switch to some predetermined desired position. In such apparatus, the switch operating arm is attached to an operating shaft and is held thereby in some predetermined angular position. The operating arm is moved from this predetermined position upon engagement of the switch arm with a fixed surface located in the path of movement of the equipment. The predetermined or equilibrium position of the switch arm is usually maintained by a spring or the like acting on the operating shaft. The angular position of the operating arm relative to the shaft is usually adjustable so that the switch arm can be used in different installations without structural modification. To this end, it is customary to knurl a portion of the surface of the switch arm or lever that is adjacent the axis of rotation thereof. Means are provided to press this surface against the knurled surface of a disc that is keyed to the shaft that is to be operated by the lever. It can be seen that with this mode of attachment, any desired angular disposition of the lever can be effected by temporarily loosening the pressing means, relatively rotating the knurled surfaces until the desired angular position of the arm is obtained and thereafter tightening the pressing means to press again the knurled surfaces into driving engagement.

Where operating arms of the foregoing type are required to function in a magnetic field, the maintenance of the equilibrium position of the operating arm until the desired engagement between said arm and the fixed surface occurs is much more difficult of attainment. This is because the magnetic field, acting on the lever, exerts a torque that unbalances the equilibrium of the lever and causes premature movement thereof away from the desired predetermined position. While it is apparent that the foregoing difliculty can be overcome by making the lever or arm of some non-magnetic material, the resulting construction is unsatisfactory due to the fact that non-magnetic materials are not susceptible of knurling in any inexpensive or commercially feasible manner.

It is therefore an object of this invention to provide a switch arm or operating lever that is not responsive to magnetic fields and yet is provided with a surface adjacent the axis of rota- 3 Claims. (Cl. 287-5232) tion that is easily knurled so as to render the angular position of the arm readily adjustable.

Other objects and advantages of this invention will be apparent upon consideration of the following detailed description of a preferred embodiment thereof in conjunction with the annexed drawing in which:

Figure 1 is a view partially in elevation and partially in vertical section of a switch arm showing the switch actuating shaft;

Figure 2 is a perspective view of the switch. actuating shaft of Figure 1; and

Figure 3 is a view taken along the line 3-4 of Figure 1.

Referring to the drawings with greater particularity, a switch operating shaft lll comprised of a cylindrical shank portion I I, an intermediate portion [2 of generally rectangular cross section, and an externally threaded end portion I3 is connected by any conventional means to a switch, not shown, so that upon angular displacement of the shaft ID the switch is biased to a desired position. The cylindrical portion ll of the shaft I0 is mounted for rotation in a housing M with a portion thereof as well as the portions l2 and I3 projecting in the manner shown in Figure 1. Fitting over the portion l2 of generally rectangular cross section is a coupling disc l5 having one knurled face and one smooth face. The disc I5 is provided with a central aperture conforming in outline to the portion I! of the shaft l0. Thus, the disc l5, when mounted as shown in Figure 1, has a portion of its smooth face abutting the shoulder l6 defined b the end of portion ll of the shaft I0 and is non-rotatably mounted on said shaft. The remainder of the smooth face of the disc ['5 rests against the surface of a plain washer I'l disposed on the portion ll of the shaft l0 between the disc l5 and the housing IA. The washer I1 is provided with a round central aperture adapted to fit with clearance over the cylindrical portion H of the, shaft l0.

Bearing against the knurled face of the disc; I5 is the knurled portion l8 of a switch arm |9. The switch arm I9 is provided with an aperture. so that it may be mounted for angular displace-- ment about the end portion [3 of the shaft 10., To establish a driving connection between the: switch arm [9 and the shaft H], the former is; placed in the Figure 1 position with its knurled; portion l8 facing the knurled portion of the disc I5. The knurled portion I8 is held in driving engagement with the corresponding portion of the disc l5 by a nut 20 that is threaded over the end portion l3 of the shaft l0 and drawn against a lock washer 2| which, in turn, bears. against switch arm l9.

At the end of the switch arm l9 remote from the connection to shaft [0, a stud 22 projects It can now be seen that the device of Figure l: may be used as an operator for a limit switch mounted on movable apparatus and that after predetermined movement ofi'such- -apparatus the.

switch arm roller 24 may engageysome-stationary part in the path of movement in orderto cause, the switch arm to move from one angular positionto another thereby to cause a change i itheacona dition of some circuit that is to be controlled.

It is to be understoodthat the shaft H's-nor mally held in one predetermined position by spring means or the like: ofi conventional: design andthat it is displacedg from this' position; by movement of the switch, arm I19: The arm [Brand the shaft it are keyed together by the. engagement 'of the knurledv portion I'B of; the arm [:9 with the knurled-portion of the'disc [5 which in turn is mounted for rotation. with shaft I13; This being the case, it is apparent that the angular disposition of the arm I'9-withrespectto the-shaft I0 can be easily adjustedtby merely loosening the nut 20 and disengaging the knurled portions: of the switch arm I9. and the'disc l5. The switch arm I 9 is then rotated'tmthedesired position and the nut 20 is again tightened.

A switch arm of the foregoing type when used under ordinary conditions may be made in a single piece of magnetic material such as iron or steel; It has been found, however, thatsuch switch arms, when used in-astrong magnetic field; are biased by the action of the field so-that the predetermined position isnot maintained until the roller 24 contacts some element that is supposed to cause the switch arm to move to-a: dif-. ferent positionv Furthermore, the non-magnetic materials may not be used because they cannot be provided with a satisfactory; knurled portion at 18.

It has been discovered; as apart-of 'thisinvention, that the foregoing difiiculties maybe-overcome by making switch armt9: of non-magnetic material except for knur1ed-"inserted'=portion I8 The knurled portion I8 is madein: the'form of a generally circular insert as. shown in Fig; 3'and fitting in a recess ofcomplementary configuration provided in the-arm. I 9; The por-tionl8 of magnetic material is brazed in position and provided with a knurled surface. This construction islvery advantageous-in that the magnetic material' of-which the portion I8? is madamay be read"- ily knurled, but because it surrounds the-portion it of the shaft l0, thereis little or no tendency for a magnetic field to cause the switch arm to move in an angular sense about the axis: of'the shaft [9. This is true=becauselanz approximately equal portion of, magnetic material isdisposed in all radial directionsf-rom the center of the end portion I3 of the shaft: t0; Thus, thereishnu momenttending to cause rotationiincidentatoexs posure for operation, in. magnetic fields;. the: en:- tire, arm being, maintained; in; equilibrium until 4 displaced by engagement with some fixed element in 'theqpath'of movement; pf the apparatus on which thearm and assembly is mounted.

It will be understood that the foregoing general description is exemplary and explanatory of the inyention, but that the invention in its broader aspects is not limited to operating arms for switchesrbut may. comprise operating levers for other-types of apparatus.

What is claimed, is:

1. Operating-means comprising a rotatable shaft, ai -arming effecting angular displacement of said shaft, said arm being of non-magnetic -material, and means connecting said arm to said shaft, and means including an insert of magnetic materiahafixed; to; said; arm and? substantially uniformly.- distributed about the axiseof'said shaft and: means securedto said rotatable shaft and cooperating with said: insert. toestablish a drive ingi connection; between said; arm and said: shaft.

2; Operating means comprising a rotatable shaft, an arm of non-magneticmaterialnfor'efiectin-g angular displacement of said shaft, and meansv connecting said arm to said shaft, said means-comprising: a disk keyed toisaid shaft, an insert attached to said arm, meanstfor pressing -a surface of: saidr insert againsta surface of said disk to establish connection between the shaft and the arm, said insert being- 0f magnetic material and being substantially uniformly distributed aboutrthe axis of" rotation ofsaid shaft whereby the: arm retains its equilibriumin a magnetic field;

- 3.. Operating means comprising a rotatable shaft, an arm offnon-magnetic material foreffecting angular displacement of" said shaft, said arm being mounted-on anend ofsaid shaft, and means. adjustably connecting said arm to said shaft, said means comprising a disk keyed t o sald shaft, said -di'skhaving a knurled surf'ace, aninsert permanently secured tosaid arm, said'insert having: a knurled surface arranged to contact the knurled-surface of said disk, andmeans'for-press inga surf-ace-of' said insert against a surface of said disk to establish-a driving connection-between the shaft and the arm, saidinsertbeing of mag neti'c material and being substantially uniformly distributedabout the-axis of rotation-of saidshaft whereby the arm-retainsits equilibrium in amag= netic field.

- GLENN C: IBIGGS.

REFERENCES; CITED;

The following references are ofi'recordin. the

, E'III'A'JPES PATENTS;

FOREIGN. PATENTS Country: Date' Number:

Switzerland; July 1', 1941, 

